Heat Exchange Network Synthesis And Optimization For Batch Process Considering Scheduling

Currently,the trend of economic globalization is increasingly prominent.Process industry is faced with the challenge of diversified product demand and complicated external environment.Batch process has developed quickly due to its intrinsic flexibility and adaptability.However,environmental pollution and energy shortage are increasingly serious with the development of the industrialization.This makes to save energy and reduce pollution is imminent and heat integration is an effective measure.This paper focused on heat integration in batch process.The initial heat exchange network(HEN)was synthesized by heuristic method.Progressive evolution rules were proposed to optimize the HEN structure.By introducing scheduling into heat integration,the effect of scheduling on direct heat recovery was analyzed.At last,the scheduling and HEN synthesis for multi-period batch process considering market demand was proposed.The main contents and results of this paper are as follows:(1)The initial HEN was synthesized by time slice model.The initial HEN may have some redundant heat exchangers,complex stream splits and unreasonable heat exchanger areas.To solve this problem,the progressive evolution rules were proposed in this paper.The evolution was conducted among the intervals one by one based on Excel.The interaction between each interval was fully considered.The total annual cost was further reduced by the trade-off between utility cost and equipment cost.The HEN was simplified by breaking the heat recovery loop and shifting heat load along the path.The total annual cost was calculated after each step to determine the merits of the new HEN.A case was calculated to illustrate the feasibility and effectiveness of structure evolution.(2)Batch process heat recovery potential is restrained by temperature difference and time.Scheduling was introduced into batch direct HEN synthesis in this paper.By using overlapping operation and adjusting the limited cycle time,the equipment idle time was reduced and the opportunity of direct heat exchange was increased.Streams that can't direct exchange heat originally may realize heat integration without heat storage.On this basis,introducing parallel devices can break the time bottleneck of overlapping operation.The opportunity of direct heat exchange increased and more heat can be recovered.The productivity can also be enhanced and more product can be produced in the same time.Two cases were calculated to analyze the impact of scheduling on batch HEN synthesis and illustrate the effectiveness of the proposed approach.(3)When the market demand changes,production can be adjusted according to reasonable scheduling.But HEN can't adapt to the scheduling changes.To solve this problem,multi-period scheduling and HEN synthesis were proposed in this paper.The manufacturing process was divided into several periods according to the market demand fluctuation.The production capacity can keep synchronized with market demand by scheduling.Thus,the batch plant can deal with the fluctuation of the market demand and keep the capital flow and inventory at a reasonable level.Heat exchange units share strategy were proposed and multi-period HEN which can satisfy the heat exchange demand with the scheduling varies was synthesized.A case was calculated to illustrate the feasibility of the proposed approach.